Now that .NET 4.0 and Visual Studio 2010 are in full swing, I think it's wise to open a page to jot down the useful add-ons that can enhance the developer experience. As time goes by, this list will get updated.
"Visual Studio 2010 runs faster when the Windows Automation API 3.0 is installed ..... Applications that use Windows Automation APIs can significantly decrease Microsoft Visual Studio IntelliSense performance if Windows Automation API 3.0 is not installed. For example, the Windows pen and touch services can significantly decrease Visual Studio IntelliSense performance if Windows Automation API 3.0 is not installed."
"A set of extensions to Visual Studio Professional (and above) which improves developer productivity."